1. Field of the Invention
The present invention relates to motors and methods for manufacturing motors in which a coil winding is wound on each salient pole in a plurality of layers.
2. Related Background Art
Motors in recent years are often structured to make them thinner and smaller. For example, an inner rotor-type thin motor used in a magnetic disk device or a hard disk drive (HDD) shown in FIG. 10 is generally made up of a stator section 10 and a rotor section 20. The stator section 10 is provided with a stator core 13 and coil windings 12 wound on the stator core 13, which are provided on an outer circumference upright wall section of a generally flat pan-shaped frame 11, as well as a pair of ball bearings 14 attached on an inner circumference surface side of an inner circumference upright wall section (i.e., a bearing holder) of the frame 11. A rotary shaft 21 of the rotor section 20 is supported in a freely rotatable manner via the pair of ball bearings 14. A generally cup-shaped rotating hub 22 is provided on the rotary shaft 21 in a unitary fashion. A magnetic disk 23 mounted on the outer circumference section of the rotating hub 22 is held immovably by the pressing force of a damper 24 screwed and fixed to the rotating hub 22.
The stator core 13 is made up of a plurality of stacked layers of magnetic plates 13a, which are shaped as shown in FIG. 11, for example, and forms a core body structured as shown in FIG. 12. By mounting a plurality of resin outer circumference guide members 13b, such as shown in FIGS. 13 and 14, on such a staked layered core body, a structure as indicated in FIGS. 15 and 16 is obtained. A common connection section 13A extends in a ring shape on the outer circumference side of the stator core 13, and a plurality of salient pole sections 13B radially protrude from the common connection section 13A, as shown in FIGS. 17 and 18. Each coil winding 12 is wound around a rib section 13B1 that makes up each of the salient pole sections 13B.
Each of the coil windings 12 has a winding section 12a that is wound in a regular winding, for example, along the rib section 13B1 of the corresponding salient pole section 13B. Each of the winding sections 12a is formed by a regular winding that begins at the common connection section 13A side of the stator core 13, turns back just before a magnetic converging teeth section 13B2 provided at the tip side of the corresponding salient pole section 13, and to the common connection section 13A side. By having a set of such regular back and forth winding repeated at least once, each of the coil windings 12 is structured to overlap in a plurality of layers.
A lead wire 12b that extends from a winding end part of each winding section 12a, which is wound in a plurality of layers, is guided and placed along the corresponding guide section 13b, which is mounted on the common connection section 13A, to be led from one salient polo section 13B to another salient pole section 13B. For example, in a three-phase motor with phases U, V and W, one of the winding sections 12a is wound continuously via the corresponding lead wire 12b from the winding beginning (U1, V1 or W1) to the winding termination (U3, V3 or W3), as shown in FIG. 19.
In the wire section 12a of each coil windings 12 in such a conventional motor, winding begins at the common connection section 13A side of the stator core 13 and returns to the common connection section 13A side to form two layers in one back and forth winding, which comprises one unit. This results in a limitation in that the winding sections 12a of the coil windings 12 can be wound only in even number of layers. As a result, even if space in the height direction of winding (i.e., in the motor's axial direction) provides for “three layers” of winding, in reality only “two layers” can be wound, for example. This causes the torque constant Kt to fall or the drive current to increase, which leads to increased power consumption.
In such a situation, the torque constant Kt can be increased by using a smaller coil diameter to increase the number of layers. However, since this would lead to higher winding resistance, the power consumption would increase significantly. In other words, in forming a winding section, a coil winding with appropriately large diameter in relation to a certain amount of winding space must be wound in as many layers as possible.
There is a conventional technique to achieve three layers (i.e., an odd number of layers) of coil winding by utilizing a core side surface. However, the conventional technique proves to be difficult to implement in reality. According to the technique, for example, a coil like a crossover line placed along the core side surface must be fixed to the core side surface before winding a winding section. This would be an extremely difficult work to implement in reality. Furthermore, even if it were possible to fix the coil like a crossover line before winding, the winding work would have to take place over the coil like a crossover line. This, therefore, would entail a problem of not being able to achieve favorable regularity, particularly in regular windings.